I have a 6” Starrett steel rule I use a lot, as well as a 4” Starrett double square. Sometimes I’ll use my 1-2-3 MicroGauge I bought it for tool setup, but find it very useful for setting bit/blade heights as well.

I have a digital caliper I use a lot, but I’ve found it difficult to use for setting bits/blades.

I have a Johnson 12” steel combination square. I was hoping for more accurate measurements. Not OCD accuracy, but within hundredths… FWIW, the Johnson combination square rule rusted VERY quickly and is now pretty much mostly brown / orange colored and very hard to read. I need to dunk it in Evaporust to get it back to speed…

On the TS I use scraps of plywood…set next to the blade, raise/lower until I’m happy with my thumbnail. I only use a router overhand and that’s just trial and error for me…set high on the initial pass and then dial down. I only use PC routers so it’s pretty easy…the increments are minute.

Set the blade extension to my depth of cut, put the end of the blade against the table or sled floor, and raise the blade or bit until it makes contact. It usually helps to rock the blade or rotate the bit and listen / feel for a scrape.

On another note, I usually don’t see it as all that big of a deal if my 1/2” deep dados are 31/64, 1/2, or 33/64 deep, as I cut them all at once.

For those occasions like lock miter or cope and stick bits, that need a precise setting, once it’s perfect, I’ll normally make a UMHW or MDF setup block for next time.

Yet another thought is to make sure any sleds you use have floors that ride on the surface of the machine, not the bottoms of miter slots. If a sled rides in the slots, varying operator pressure can affect dado depth.

I use a scrap piece for the initial cut. Usually a piece of scrap oak, so I get a nice cut. Measure, adjust as needed. Just put in a .020” groove in the side of a guitar for binding that way. Just kept making micro adjustments until the binding fit the scrap cut perfectly. Cut the groove in the guitar, mounted the binding. Perfect. For other more gross measurements, like others, I keep multiple 6” Starrett rulers and squares lying around, bought over the years. Always have more than one, since I lay things down….(old age)

I figured that out making the picnic table I HATED making. The top boards had to be spaced 3/8 a part. I was looking around the shop and thought “there has to be something in there that’s 3/8”. Then it dawned on me do grab a drill bit. After that I had the same forehead slapping session remembering all the time I wasted trying to set bit/blade heights when I had a box of “precise set up blocks” in virtually any size I ever needed.

Funny thing is, 3/8” is the most common setup height for non through cuts for me as I like to cut my dadoes halfway through 3/4” stock… And I have plenty of extra 3/8” bits (I kept losing them, buying replacements, lather rinse repeat until they all sort of showed back up one day!)

Be careful, a machinist once taught me that drill bit shanks are not reliably sized, just the cutting flutes (which make a reliably sized hole). So you might double check with a set of calipers before you use a drill bit shank to set your blade/bit height. Then again, I don’t think it would be off more than a couple thousandths, so shouldn’t really matter.

That’s what I do. I bought a large cheap index set on Amazon after my revelation. I never drill with them, just set up tools. I measured them with dial calipers before using them and they were extremely close (within a thousandth). That doesn’t solve the problem that just because I think half of 3/4” is 3/8” that it actually is. I still always do test cuts unless I am 100% sure I want the depth chosen, then I just go for it. I’ve used these enough to trust them.

I made a set of set up blocks from Jatoba drum sanded to exact thickness. Finding TDC on the tablesaw is critical so I usually lay a straight edge across my set up block and raise the blade while turning it until it just kisses the straight edge. Then I ALWAYS cut a piece of scrap to confirm the setting. I have used drill bit/router shanks for spacers when setting up my box joint jig but have learned that all 1/4” shanks are not the same.

Being really OCD, I have a number of measuring devices that are very accurate, and use whichever one is the easiest. But the best one, is a piece of scrap wood cut up to make sure that my setting is accurate. I also make MDF setup blocks for odd measurements to use for the rest of the project.

Also, Incra rules, setup blocks, etc. The Incr rules, the ones with the holes for the pencil, are the most used item in the shop. But right behind it is the Wixey digital calipers. As a result, most of my little projects are fairly solid just with the dry fit.

I’ll be honest…...I really like making precise cuts and measurements. It is part of the fun for me. Not always practical, but fun….....(-:

If you take a straight and flat stick/ruler and divide it into equal lengths, you can reliabily get an accurate fraction of the thickness of your stock.

Say you want a dado that is 1/2 the depth of your workpiece. You take something flat, divide it into 2 equal sections (with a line at the halfway point). One end goes on your workpiece edge, one end is touching the table. Raise the saw blade/router bit until it just touches the line on the bottom of the piece.

If you want it at 1/3 deep, divide it into 3 sections, and use the line closest to the table rather than the one closest to your stock.

-- The quality of one's woodworking is directly related to the amount of flannel worn.